Rotary dryer drum having closed internal channels

ABSTRACT

D R A W I N G A ROTARY, CYLINDRICAL DRYER DRUM WITH A PLURALITY OF INTERNAL, CIRCUMFERENTIAL CHANNELS. THE CHANNELS ARE PROVIDED BY CIRCUMFERENTIAL GROOVES FORMED IN THE INNER SURFACE OF THE SHELL OF THE DRYER AND INCLUDE CONDUIT-DEFINING MEANS DISPOSED WITHIN THE GROOVES. EACH OF THE CHANNELS FORMS AN ANNULAR CONDUIT AND INCLUDES AN INLET FOR INTRODUCING A HEAT TRANSFER FLUID INTO THE CHANNEL AND AN OUTLET FOR REMOVING THE HEAT TRANSFER FLUID FROM THE CHANNEL.

Jan.'12, 1971 G, o. CARRIER ETAL' 3,553,849

ROTARY DRYER DRUM HAVING CLOSED INTERNAL CHANNELS Filed Dec. 15, 1968 rI 2 Sheets-Sheet 1 \lma 47 INVENTORS George 0. Churrier- Gene R. WolfeATTORNEY Jan. 12,1971 3, R ETAL 3,553,849

ROTARY DRYER DRUM HAVING CLOSED INTERNAL CHANNELS Filed Dec. 16, 1968 2sheets-sheet 2 Fig. 3

Fig.4

Fig. 5

INVENTORS George 0. Chorrier Gene R. Wolfe A T TORNE Y United StatesPatent 3,553,849 ROTARY DRYER DRUM HAVING CLOSED INTERNAL CHANNELSGeorge 0. Charrier, Cincinnati, and Gene R. Wolfe,

Hamilton, Ohio, assignors to The Procter and Gamble Company, Cincinnati,Ohio, a corporation of Ohio Filed Dec. 16, 1968, Ser. No. 784,043 Int.Cl. F26b 11/02 US. Cl. 34-124 8 Claims ABSTRACT OF THE DISCLOSUREBACKGROUND OF THE INVENTION This invention relates to rotary,cylindrical dryer drum structures and more particularly to a rotary,cylindrical dryer drum structure wherein an internally grooved dryershell is provided with conduit-defining means positioned in the groovesto form annular conduits in the shell.

Heretofore, rotary dryer drums employed in papermaking apparatus havebeen extremely ponderous structures, principally because the steamutilized to heat the drum, and thereby dry the paper which passesthereover, was introduced directly into the interior of the drurln,thereby subjecting the entire drum structure, both shell and heads, tothe combined pressures and thermal effects of the hot steam. As aresult, both the shell and the heads of the drum had to be massivestructures to withstand such stresses. As the shell thickness isincreased to Withstand the higher steam pressures necessary for moreeflicient drying, the rate of heat tranfer through the shell is reducedbecause of its increased thickness.

In addition to the effects on the shell itself, the pressure and thermaleffects of the steam have a particularly adverse effect at theshell-head junctions, where the loading and resultant stress pattern isparticularly complex, and generally require that a large, tapered flangebe formed at the end of the shell in order to withstand the stressesoccasioned by the end loads that are applied at this particular portionof the shell by the deflection of the heads of the drum. However,tapering the shell end flanges reduces the heat transfer rate at the endof the shell and thus either longer dryers are needed or the width ofthe web must be reduced to assure uniform drying across the entire widthof the web being dried.

Various approaches have been proposed to improve the heat transferthrough the shell while not unduly compromising its structuralintegrity. For example, Justus et al. in US. Pat. 3,241,251 disclose arotary dryer drum structure which includes a plurality of internal,circumferential grooves on the inner surface of the shell to reduce theeffective thickness thereof for heat transfer purposes and yet to retainthe thickness necessary for structural purposes. Although the structureshown and described in the Justus et al. patent is eminently suitablefor drying paper Webs, it has been found that the circumferentialgrooves cannot be carried to the extremes of the drum because of thehereinabove-discussed stress pattern that exists at the shell-headjunction. As a result, the entire surface of the drum cannotsatisfactorily be used for uniformly drying paper because of thenon-uniformity in drying rate across the drum, and the web to be driedmust thus be confined to a width less than the entire width of the outershell of the drum. However, the heat transfer at the junction of thehead and shell can be further improved by employing transverse groovesin the shell flange as shown and described by Vonderau in US. Pat.3,258,851.

In spite of the improvements in drying structures taught by thosepatents, the heat transfer medium, which is the case of paper dryers isgenerally steam, is still introduced directly into the interior of thedrum and contacts both the shell and the heads, Since the contact need.only be made the shell, through which it is desired that the heattransfer take place, the heating and pressurizing of the heads isunnecessary and contributes to the weight and cost of such dryersbecause the heads must be designed and fabricated to withstand the highpressure and thermal loads imposed thereon, and the shell ends must bedesigned with the head deflections and loads in mind. In addition to theweight and costs aspects of such dryers, the pressurization of a largerotating drum can pose significant safety problems.

SUMMARY OF THE INVENTION Briefly stated, in accordance with one aspectof the present invention, a rotatable, cylindrical dryer drum isprovided which comprises a cylindrical shell and a head at each end ofthe shell to close the same, the heads including means for rotatablysupporting the drum and means for introducing and removing a heattransfer medium to and from portions of the interior of the drum. Theshell has a plurality of internal circumferential grooves formed thereinand has conduit-defining means disposed Within those grooves fordefining annular conduits to insure close proximity between the shellheat transfer surface and the heat transfer medium. Means are providedfor introducing a heat transfer fluid into each of the annular conduitsand for removing the heat transfer fluid therefrom.

It is an object of the present invention to provide a rotary dryer drumconstruction having improved heat transfer characteristics and improvedsafety with attendant reductions in both the cost and the weight of thedryer.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a longitudinalcross-sectional view of a rotatable, cylindrical dryer drum according tothe present invention showing the various internal and external partsthereof in operative relationship.

FIG. 2 is a cross-sectional view taken along the line 2-2 of FIG. 1.

FIG. 3 is an enlarged, fragmentary cross-sectional view of a portion ofthe shell taken along the line 3-3 of FIG. 2 and showing the annularconduits formed in the shell and one form of conduit-defining meanspositioned therewithin.

FIG. 4 is an enlarged, fragmentary cross-sectional view of a portion ofthe shell wall showing a form of conduitdefining means positioned withinthe grooves and a means for introducing the heat transfer fluid to theannular conduits thereby formed.

FIG. is an enlarged, fragmentary cross-sectional view similar to FIG. 4but showing a means for removing the heat transfer fluid from theannular conduits.

FIG. 6 is a fragmentary cross-sectional view showing an alternativeconduit-defining means positioned within a groove for defining anannular conduit therein.

FIG. 7 is an enlarged, fragmentary cross-sectional view showing anotherconfiguration of conduit-defining means positioned within the grooves.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to the drawingsand particularly to FIGS. 1 and 2, there is shown a dryer drum 10 of thepresent invention formed from a hollow cylindrical shell 11 ofpredetermined axial length. Shell 11 can be made of cast iron or thelike and has circumferential grooves on its inner surface, as morecompletely described hereinafter. The grooves and their inlet and outlettubes are not shown in FIGS. 1 and 2 because size relationships wouldrender their representation diflicult. The ends of shell 11 can beclosed by means of heads 12 and 13, which can be inwardly dished asshown and which can be secured to the ends of shell 11 at shell flanges14 as by means of bolts 15. Heads 12 and 13 can be of substantiallyannular construction and can have a central opening to which isconnected a central shaft 16 as, for example, by means of bolts 16a.Central shaft 16 is preferably hollow and is provided in two distinctportions 18 and 19 as shown in FIG. 1. Extending from the ends ofcentral shaft 16 are a pair of journals 20 and 21 which are adapted tobe carried in trunnions (not shown) so that the drum can be rotated.When central shaft 16 is divided into two portions, an imperforate,pressureand temperature-resistant divider member 22 is positionedtherebetween to define two separate chambers 23 and 24. Chambers 23 and24 are in communication with the outer ends of journals 20 and 21,respectively, by means of passageways 25 and 26 through journals 20 and21, respectively.

A hollow tube 27 mounted on central shaft 16 provides communicationbetween chamber 23 and tubular distributor 28, the structure andfunction of which will be explained in further detail hereinafter. Theheat transfer fluid is admitted through passageway 25 in journal 20 tochamber 23 through tube 27 and to distributor 28. Similarly, a hollowtube 29 is connected with chamber 24 to provide communication betweenchamber 24 and condensate return header 30, the structure and operationof which will also be illustrated and described in further detailhereinafter. The position of condensate return header 30 can be radiallyadjusted by means of supporting stud 31 which has a pair of locking nuts32, 33 that can be loosened and turned to change the radial position ofcondensate return header 30. Condensate return header 30 is incommunication with passageway 26 in journal 21 through chamber 24 andsupport tube 31.

Cylindrical shell 11 has a plurality of circumferential grooves on itsinterior surface as shown in FIG. 3. The grooves are defined by thespaces between adjacent circumferential ribs 34. Positioned within thegrooves are means for defining an annular conduit therein such as, forexample, metallic tube 35 positioned in the lowermost portion of thegroove as shown in FIG. 3. Tube 35 is preferably rigidly positionedwithin the groove and in intimate contact with the bottom thereof. Suchintimate contact can be achieved by actual face-to-face contact of thematerials comprising the tube and the shell 11 at the bottom of thegroove, or alternatively, by interposing a readily conformable hightemperature adhesive between such materials, or by means such as weldingor brazing the materials together in such location. It is important thatthere be a continuous conduction path, without any substantial amount ofintervening air space or other material between the exterior of tubes 35and thelowermost surfaces of the grooves in shell 11 in order to insuregood heat transfer from the heat transfer medium to the external surfaceof shell 11.

Each of tubes 35 forms a conduit for the heat transfer fluid, which canbe steam or any other heat transfer medium. Since only tubes 35 carrythe pressure load imposed by the heat transfer fiuids, the thickness ofshell 11 and that of heads 12 and 13 of the dryer need not be as greatas they would otherwise have to be. In fact, the heads need not beclosed and can be replaced by other supporting structure, such as forexample, spokes.

As shown in FIG. 4, the steam or other heat transfer fluid is conveyedto the annular conduits through a plurality of inlet tubes 36 whichprovide a communication path between annular tubes 35 and distributor28. Similarly, as shown in FIG. 5, the heat transfer fluid, or in thecase of steam the condensate, is removed from annular tubes 35 by meansof a plurality of outlet tubes 37, each of which is slidable in tube 35and provides a path of communication between a single annular tube 35and condensate return header 30. When steam is the heat transfer fluidoutlet tubes 37 are so positioned with respect to annular tubes 35 thatone end of the former is relatively close to the portion of annular tube35 which is closest to the outer surface of shell 11. The reason forthis positioning is that during rotation of the drum, centrifugal forceurges the condensate to the portion of annular tube 35 closest to theouter surface of the shell 11 and thereby presents a heat insulatinglayer which impedes the flow of heat from annular tube 35 to the outersurface of shell 11. It is desirable that the layer of condensate beremoved to the greatest extent possible to permit unimpeded heattransfer. If positioned otherwise when steam is the heat transfer fluid,the condensate would not be removed from a tube 35 until it accumulatedsufliciently to reach the radially outermost end of the associated tube37.

From the foregoing description and the accompanying drawings, it can beseen that, in operation, steam is introduced through passageway 25 injournal 20 to chamber 23 and is carried by inlet tube 27 to distributor28, whereupon it is conveyed to annular tubes 35 by means of inlet tubes36 interconnecting annular tubes 35 and distributor 28. Since eachannular tube 35 has a separate inlet tube interconnecting it withdistributor 28, each annular tube 35 receives steam having substantiallythe same physical and thermal properties. As the steam passes throughannular tube 35 and condensation takes place, the outlet tubes 37, whichare preferably positioned opposite the inlet tubes 36 in order tobalance the drum, convey the condensate from the annular tubes 35 tocondensate return header 30 and thence to outlet tube 29 and throughchamber 24 and passageway 26 in journal 21 by means of suction which isimposed by a vacuum pump (not shown). Thus the heat transfer fluid fromone annular tube 35 does not pass into any other such annular tube andsince the conditions of the steam in each annular tube 35 aresubstantially the same, the configuration herein described provides adryer drum having a substantially constant temperature profile acrossits outer surface. Furthermore, since the heads of the dryer are notsubjected to the pressure and temperature effects of the steam, theheads do not impose as great a load at the head end of the shell andthus the annular tubes can be positioned closer to the ends of the shelland thereby provide uni-.

form heat distribution across substantially the entire axial length ofthe dryer drum.

Whereas the groove configuration shown in FIG. 3 has substantiallyparallel radial walls, another confiuration for the walls of the grooveand for the conduit-defining member placed therein is shown in FIGS. 6and 7. As therein shown in cross section, the groove, which issymmetrical and of an inverted keyhole-like shape, has a rectangularopening defined by radial walls 38 followed by sharply outwardly anddownwardly sloping walls 39 which intersect gradually tapering inwardlyand downwardly extending walls 40. The lower ends of walls 40 areseparated by a distance substantially equal to the width at the openingportion, and meet downwardly and outwardly tapering walls 41 which aretangential to curved portion 42, the lowermost part of the groove. Anannular, conduit-defining member 43, positioned within and retained bythe groove, has a cross section which corresponds with a portion of thecross section of the groove. The lowermost portion of member 43 hasoutwardly depending skirts 44 which are forced against downwardly andoutwardly tapering walls 41 of the groove when pressure is applied inthe conduit, thereby increasing the pressure and improving the sealtherebetween. Annular conduit-defining member or seal 43 is preferablyretained in position by a retaining member to prevent it from beingdislodged from the groove by the pressure of the heat transfer fluid. Acontinuous coil spring 45 having an oval cross section as shown in FIG.6 can be used for this purpose. Alternatively, annular conduit-definingmember 43 can be retained in position by a plurality ofcircumferentially spaced, generally V-shaped spring members 46, as shownin FIG. 7. The stiffness of conduit-defining member 43 can be increased,if desired, by forming it around a stiffening member 47 which can be offlexible metal or the like.

Preferably, annular conduit-defining member 43 is formed from resilientmaterial to permit the hereinbeforedescribed pressure effect to assistin seating the member against the sidewalls of the groove and improvethe seal therebetween. The retaining member serves to retain the annularmember in position and prevent it from being forced from the groove bythe steam pressure within the conduit. Annular conduit-defining member43 can be molded from a resilient, high-temperature resistant rubbercompound such as a silicone rubber, or it can be formed from afluorocarbon resin such as polytetrafluoroethylene or a copolymer oftetrafluoroethylene and hexafluoropropylene. Tubes 36 and 37 passthrough annular member 43 and because of the resilience of member 43when formed from rubber or the like, a tight seal is provided betweenannular member 43 and tubes 36 and 37. In the embodiment shown in FIG.7, the tubes 36 and 37 pass through stiffening member 47 and springmembers 46.

While particular embodiments of the invention have been illustrated anddescribed, it will be apparent to those skilled in the art that variouschanges and modifications can be made without departing from the spiritand scope of the invention and it is intended to cover in the appendedclaims all such changes and modifications that are within the scope ofthis invention.

What is claimed is:

1. In a rotatable dryer drum comprising a cylindrical shell, and meansfor rotatably supporting said cylindrical shell, said cylindrical shellhaving a plurality of internal, circumferential grooves formed therein,an improved heat transfer fluid conduit system comprising:

(a) conduit-defining means disposed within said grooves for definingimperforate annular conduits therein in close heat transfer relation tosaid shell;

(b) means for introducing a pressurized heat transfer fluid into saidannular conduits, said introducing means comprising imperforatepassageways connecting an exterior source of said heat transfer fluid tosaid annular conduits; and

() means for removing said heat transfer fluid from said annularconduits, said removing means comprising imperforate passagewaysconnecting said annular conduits to a point exterior of said drum, saidpassageways of said introducing means and said removing means beingspaced from said shell whereby said shell of said drum maybe heated bycirculating pressurized heat transfer fluid through said conduit systemwithout pressurizing non-conduit portions of said shell.

2. The dryer drum of claim 1 wherein said conduitdefining meanscomprises an annular metallic tube secured to the lowermost portion ofsaid groove to provide a conduction path between said heat transfermedium and the external surface of said shell without an intervening airspace.

3. The dryer drum of claim 1 wherein said conduit defining meansconsists of annular seals conforming in cross section to radially inwardportions of the cross sections of said grooves to permit retention ofsaid seals in said grooves, whereby said annular conduits are formed bythe seals and the portions of said grooves located radially outwardlyfrom said radially inward portions of said grooves.

4. The dryer drum of claim 3 including separate retaining means forholding said conduit-defining means in a predetermined position withinsaid grooves.

5. The dryer drum of claim 4 wherein said conduitdefining meanscomprises a resilient annular member including internal stiffeningmeans.

6. The dryer drum of claim 5 wherein said retaining means comprises aspring member which cooperates with the sides of said grooves to retainsaid annular member in position.

7. In a rotatable dryer drum comprising a cylindrical shell, means forrotatably supporting said cylindrical shell, said cylindrical shellhaving a plurality of internal, substantially parallel circumferentialgrooves formed therein, the improvement comprising a heat transfer fluidconduit system comprising:

(a) conduit-defining means disposed within said grooves in close heatconduction relation thereto for defining a multiplicity of substantiallyimperforate parallel annular conduits, said conduit-defining means eachincluding an inlet and an outlet, said inlets being in substantiallysymmetrical circumferential relationship with said outlets; and

(b) imperforate inlet conduit means and outlet conduit means havingpassageways associated with said inlets and outlets, said inlet conduitmeans and said outlet conduit means each extending from a point exteriorof said drum to the interior thereof, said inlet conduit means beingbranched within said drum and flowconnected to each said inlet, saidoutlet conduit means being branched within said drum and flow-connectedto each said outlet, said passageways of said inlet conduit means andoutlet conduit means being spaced from said shell, whereby a pressurizedheat transfer fluid can be circulated through said conduit systemwithout thereby pressurizing non-conduit portions of said drum.

8. The dryer drum of claim 7 wherein each said conduitdefining meanscomprises a resilient annular seal conformable in cross secton to aportion of the cross section of said grooves, and means for retainingsaid seal in said groove, whereby said annular conduits are formed bythe lower portions of said grooves cooperating with said seals.

References Cited UNITED STATES PATENTS 533,268 1/1895 Brewster 34--124X1,911,375 5/1933 Lucke -176 2,287,066 6/1942 Rogers 165-168X 2,612,3519/1952 Janos 16578 2,987,300 6/1961 Greene 165171X ROBERT O. OLEARY,Primary Examiner T. W. STREULE, Assistant Examiner

